Description (AMM 27-81-00)

 

A- High lift leading edge devices are used in combination with the trailing edge flaps to allow airplane operation from short runways. The use of leading edge devices allows a change in wing camber which greatly increases lift. The leading edge lift devices consist of four Krueger flaps and six slats (Fig. 1).

 

B- Three leading edge slats are installed outboard of the engine and two leading edge flaps are installed inboard of the engine on each wing. The slats and flaps are numbered from left to right as shown in Fig. 1. Leading edge slats 1 thru 6 are actuated by a three-position hydraulic actuator. If hydraulic pressure is low, a blocking valve will create a hydraulic lock to prevent actuator movement. This locking action will hold the slat in the position at which the loss of hydraulic pressure occurs. Each leading edge flap is actuated by a two-position hydraulic actuator.

The flap actuator will also lock in position if hydraulic pressure is low. Locking the actuators prevents blowback of the flaps and slats if hydraulic pressure is lost during takeoff or landing. Restrictors installed in the flap and slat actuator hydraulic pressure lines limit the actuating speed of the leading edge devices.

 

C- The leading edge flaps and slats are normally powered by hydraulic system B. A three-position spool-type control valve is operated by the flap control unit. The control valve ports hydraulic fluid to the leading edge flap and slat actuators. When the trailing edge flaps are between 1 and 5 units, the control valve ports pressure to fully extend the leading edge flaps and extend all leading edge slats to the intermediate position. When the trailing edge flaps are positioned to 10 units or more, the control valve ports pressure to fully extend all leading edge slats.

 

D- On flap retraction, all leading edge flaps and slats remain fully extended until the trailing edge flaps are retracted to less than 10-unit extension. Between 10 units and 5 units, all leading edge slats retract to intermediate positions, and all leading edge flaps remain fully extended. As the trailing edge flaps move from 1 unit to fully retracted position, all leading edge flaps and slats move to the fully retracted position. Control lever movement toward the UP detent is stopped momentarily at the 1-unit position by a gate on the flap control quadrant.

 

E- A standby hydraulic system is provided to extend the leading edge flaps and slats in the event hydraulic system B fails. The system is controlled by the alternate trailing edge flap switches on the overhead panel. Actuating the switches automatically pressurizes the standby hydraulic system. Pressurized fluid from the standby system is directed to the flap and slat actuators by a motor-operated shutoff valve in the standby system modular package. Fluid flow to the actuators is regulated by a flow limiting valve and a hydraulic fuse.

 

F- An auto slat system is provided to automatically extend the leading edge slats from the intermediate position to the fully extended position at a predetermined angle of attack. The slats automatically retract to the intermediate position when the angle of attack is reduced (Ref 27-83-00).